The present invention relates to a system and method for the detection of ethylene oxide in air. More specifically, the present invention relates to a technique for determining the level of ethylene in air present within one or more sample areas.
Ethylene Oxide is used in the production of solvents, antifreezes, textiles, detergents, adhesives, polyurethane foam, pharmaceuticals, fumigants, as well as sterilants for spices, cosmetics, and hospital equipment. While ethylene oxide is a necessary compound in the above applications, exposure to levels exceeding 0.5 ppm can be harmful both to individuals and to the environment. For example, studies have shown that in addition to side effects such as dizziness, nausea, and vomiting, ethylene oxide is linked to leukemia and other cancers. In addition, under certain circumstances, ethylene oxide contamination has been known to violently explode causing bodily injury and significant property damage. Accordingly, numerous types of monitors have been employed to determine the concentration of ethylene oxide in the workplace and other areas of interest.
Conventional techniques for measuring ethylene oxide in air rely primarily on the use of electrochemical sensors. These sensors operate by monitoring an electrical property, (e.g., the resistance, capacitance, dielectric, conductance, colorimetry, etc.) constant of a sensor element or solution in physical contact with a sample of air. The selected electrical property of the sensors change quantitatively as a function of the amount of ethylene oxide present in the sample gas and such changes are translated into ethylene oxide concentration measurements.
As the sensing elements in chemical sensors are necessarily exposed to gas samples, contaminants in the gas stream such as water, oils, and other airborne contaminants directly contact the sensors. While chemical sensors can, in some circumstances, provide reliable measurements for short periods of time after calibration, the exposure to the contaminants alter the electrical response of the sensor, thereby causing drifts in the calibration. This condition results in erroneous readings and can lead to eventual failure if the contaminants accumulate. Various filters (coalescing, adsorbents, and particle filters) have been employed to minimize the effects of foreign chemical/matter contamination, but historically these filtration schemes are only temporary solutions. This is due in part because the filters are easily saturated with contaminants or they leak and require replacement at irregular intervals.
Some conventional electrochemical sensors for the detection of ethylene oxide are configured to compensate for some types of contaminant that contacts the sensor head. For example, the EtOx ethylene oxide electrochemical sensor manufactured by MSA of Pittsburgh, Pa. adjusts ethylene oxide concentration measurements based on various concentrations of airborne contaminants as related to an equivalent of 1 ppm of ethylene oxide including, 3079 ppm of hydrogen, 635 ppm of carbon monoxide, 0.8 ppm of isopropanol, and 0.2 ppm of formaldehyde. Electrochemical sensors are also prone to error from polar (heavy) molecules or ionic reactions on the sensor head. Accordingly, when calibrated, the baseline “zero” measurement for electrochemical sensors take into account the potential contaminants, and the “span” measurement is made by passing a known quantity of ethylene oxide in air through the electrochemical sensor and recording values of one or more of voltage, current, or conductance. Any change in the physical response of the electrochemical sensor head results in a change in the zero and span output levels and thus, the concentration detected by the sensor. While such sensors may provide accurate measurements for a limited period of time, they require frequent cleaning and replacement.
It should therefore be appreciated that there remains a need for a precise and durable technique for detection of ethylene oxide in air.